Screened thermionic tube



SCREENED THERMIONIC TUBE- Filed 001;. 20, 1928 INVENTOR CHARLES S. FRANKUN M fla ocw o A ORNEY control grids and the cathode.

Patented July 12, 1932 UNITED STATES PATENT OFFICE CHARLES SAMUEL FRANKLIN, OF LONDON, ENGLAND, ABSIGNOB '10 RADIO CORPORA- TION OF AMERICA, A CORPORATION OF DELAWARE SOREENED THERMIONIC TUBE Application filed October 20, 1928, Serial No. 313,741, and in Great Britain October 28, 1927.

This invention relates to thermionic valves or tubes and has for its principal object to provide a thermionic valve in which the effect of inter-electrode capacity is reduced to a greater extent than has hitherto been possible.

In the known so-called screened grid valve, in which an additional electrode, adapted to act as an electrostatic screen and normally connected to earth through a source of fixed potential, such as a battery, is located between the control grid and the anode, the effects of inter-electrode capacity, though very largely reduced, are not entirely el minated owing to the fact that a capacity exists between the additional electrode and the anode. This capacity gives rise to the occurrence of high frequency currents in the additional electrode, which currents, flowing to earth through the impedance constituted by the associated connecting lead, cause high frequency variations of the potential of the additional electrode, which variations act electrostatically upon the control grid. This undesirable effect, though small, becomes increasingly important with increase in frequency.

According to this invention a thermionic valve comprises in substantially symmertical arrangement a cathode, control grids located on opposite sides of said cathode, screening electrodes located on the sides of said control grids remote from the cathode, and anodes located on the sides of said screening electrodes remote from the control grids.

Valves in accordance with this invention are intended to be used in so-called push-pull circuits, i. e., circuits in which the potentials applied at any moment to the controlling grids are equal and opposite, as also are the potentials applied to the anodes. The screening electrodes are intended to be connected together and earthed through a source of fixed potential such as a battery.

Preferably the screening electrodes are connected together within the valve and preferably also they are formed of a single structure surrounding, so far as is practicable, the

This common structure is then connected to the battery, through which it is to be earthed, by a single lead passing through the envelope of the valve.

The invention is illustrated in the accompanying drawing, in which Figure 1 shows schematically one form of construction in accordance With the invention, while Figure 2 shows diagrammatically a valve such as that shown in Figure 1 connected in circuit as an amplifier.

Referring to Figure 1, a thermionic valve comprises a cathode or filament 1 situated in a plane parallel with and between a pair of control grids 2 located one on each side of the cathode. The control grids and cathode are substantially surrounded by a screening grid structure 3 adapted electrostatically to screen the control grids and forming in effect two screens, a pair of anodes 4 being located on opposite sides and outside the screenmg grid structure. The whole arrangement is substantially symmetrical about the plane of the cathode, so that the valve in effect comprises two balanced and opposed electrode systems. A single connection 5 is made to the screening grid structure and all the leads to the electrodes should be brought out through the envelope of the valve in such a way as to minimize undesirable interconnection capacities. In the arrangement shown in the figure, 6 are the anode leads, 7 the filament leads, and 8 the control grid leads.

If desired, be provided between the anodes and the main screening grids, so as to minimize space charge effects.

Figure 2 shows the valve illustrated in Figure 1 in circuit. In this figure, 9 is a pushpull input transformer, 10 a push-pull output transformer, 11 a grid bias battery and 12 an anode battery; 13 is a screen grid battery.

It is found that valves in accordance with this invention are very free from reaction effects and may be satisfactorily employed in circuits of very high frequency.

Having now particularly described my invention, what I claim is 1. An electron discharge device comprising a sealed envelopeenclosing a cathode, a

additional screening grids maypair of independent control electrodes, one

located on each side of said cathode, a pair of independent plate electrodes, one located on each side of said cathode and adjacent the control electrode on that side of the cathode,

and a screen electrode surrounding said cathode and said control electrodes and interposed between each plate electrode and its adjacent control electrode.

m 2. An electron discharge device comprising a. sealed envelope enclosing a cathode, a control electrode on each side of said cathode, a screen electrode forming a continuous wall around said control electrodes and said cathode, and a pair of independent plate electrodes located outside said screen electrode in registry with said control electrodes.

3. An electron discharge device comprising a sealed envelope enclosing a pair of independent plate electrodes, a pair of independent control electrodes located between said plate electrodes, a cathode located between said control electrodes, and a single electrostatic screen interposed between said plate electrodes and said control electrodes and surrounding on all sides said control electrodes and said cathode with said plate electrodes outside opposite portions of said screen.

4. An electron discharge device comprising a sealed envelope enclosing a cathode, cooperating control and plate electrodes located on one side of the cathode, a second set of cooperating control and plate electrodes located on the opposite side of said cathode, and

a screen electrode surrounding said cathode and said controlelectrodes and interposed .between the control and the plate electrodes of each set of cooperating electrodes.

CHARLES SAMUEL FRANKLIN. 4o 

